COMMUNITY SANITATION 409 



proved until about 1863, although the theory had been 

 proposed one hundred years before. Among the great 

 names associated with the gradual development of bac- 

 teriology (the science of germs) are several of special 

 interest. Leeuwenhoek, a Dutch lens maker, in 1683 

 made a lens so powerful that he could see minute living 

 things in the scrapings from 

 teeth. This led to the dis- 

 covery and classification of 

 bacteria. Tyndall, the noted 

 English physicist, and the , ' 

 great Louis Pasteur in 1860 

 proved that air, when free 

 from all particles, does not FIG. SGI. Multiplication of Bac- 

 cause fermentation and decay, 



but that these effects are produced by bacteria. In 1882 

 Robert Koch invented gelatin and agar culture media 

 (nutrient substances for the growth of bacteria) so that 

 germs could be kept separated and each kind studied 

 by itself. 



From the investigations of these men and many others 

 we are now sure that germs are the cause of colds, ton- 

 sillitis, diphtheria, tuberculosis, pneumonia, measles, scarlet 

 fever, typhoid fever, smallpox, blood poisoning, malaria, 

 yellow fever, etc. If we know that all these diseases 

 are caused by germs and can learn the means by which 

 the germs may be destroyed, it is now only ignorance or 

 carelessness that will allow an epidemic to spread. 



To prevent the spread of an infectious disease several 

 things about the disease and the germs which cause it 

 must be known, namely : 



(a) The source of the germs. 



(6) Conditions favorable to the growth of the germs. 



